More than 11,000 people have been killed in South and Southeast Asia Sunday, after one of the largest earthquakes in a century struck off the Indonesian island of Sumatra. Most of the dead were victims of a tidal wave that spread out across the Indian Ocean, devastating coastal communities as far as Sri Lanka and Thailand.

The death toll continues to rise as rescue teams reach more remote coastal communities in India, Sri Lanka, Thailand, Maldives and Indonesia.

Across the region, emergency services are scrambling to rescue the injured, and provide survivors with tents, blankets, food and clean drinking water.

Indonesian presidential spokesman Andi Mallararengeng says damaged communications are making it difficult to assess the full situation.

"So, we are waiting for more accurate information," he said.

The quake, which the U.S. Geological Survey measured at 8.9, hit Sunday morning, more than 100 kilometers off Indonesia's Sumatra Island.

U.S. experts say it is the worst quake in Indonesian history, and the fifth strongest since 1900.

It sent huge tidal waves more than 1,500 kilometers across the Indian Ocean, which caused most of the damage and fatalities.

The towering waves swept clean across the low-lying Maldive Islands, leaving a trail of death and destruction in their wake.

A list of the dead at one hospital in northern Indonesia showed that many children were victims: too weak to swim, and too small to climb to one of the few safe havens.

Indonesia sits on the so-called "ring of fire," a highly active seismic band where plates of the earth's crust collide.